Since to my mind it would be extremely annoying having to "ignore" foreign players because my character is not able to communicate in other languages than his own, I'd either justify it by saying he IS able to speak more than one language (it takes quite some time to travel to Mythodea, if I got that right, so you have plenty of time to learn other languages), or simply handle it the way you suggested; ignore the fact that you don't speak your fellow players' language but pretend you did.
Quite a good question, to be honest ^^
On the one hand, getting another player to play the role of a "professional" translator - even if every participant actually does speak english - might be a chance to witness some really awesome roleplaying; on the other hand, as not everyone's most favourite language is english, it could as well lead to a lot of confusion. Which is awesome as well, but not necessarily for each and every player.
But nonetheless, depeding on your german/english skills it might be more comfortable for you to just stick to english and hope everyone can understand you. If that doesn't work, just try to get a "professional" translator doing the work and roleplaying for you.
Kind regards from Germany,
Rogan
P.S.: The last time I talked to a foreign player was on CoM '06, but instead of speaking english, I adressed him in german. In my opinion, this made his character a lot more interesting, as he had to really think about what to say and it felt all the more like a "clash of cultures" (in a positive way, though).
It was a really great experience. ^^